In recent years, in ECUs (Electronic Control Units) for a vehicle, the importance of a microcomputer (hereinafter, “micom” where appropriate) included therein has been increasing along with the enhancement of electronic control in vehicles.
For example, in a vehicle electronic control unit, a target command value is obtained in a micom and various devices related to an engine or the like are driven based on the obtained target command value. Accordingly, monitoring of operations of a micom has been proposed to ensure operations of these devices.
In Patent Document 1, a question signal 20 is transmitted from a monitoring circuit 2 to a micom 1, the micom 1 performs a self-function check calculation according to the content of the question signal 20 and transmits its calculation result back to the monitoring circuit 2 as a response signal 10. The monitoring circuit 2 then compares the content of the response signal 10 transmitted from the micom 1 to a correct answer so as to monitor whether the micom is operating normally. The question signal 20 and the response signal 10 are transmitted and received by serial communications.